Aqueous dispersions of a mixture of siloxanes and an aminoplast resin, method of coating, and article obtained



United States Patent Ofilice 3,061,567 Patented Oct. 30, 1962 This application relates to a siloxane treated paper and I its method of manufacture. It is a continuation-in-part of applicants copending application Serial No. 683,438, filed September 12, 1957, which was in turn a continuation-in-part of applicants then copending application Serial No. 554,637, filed December 22, 1955, both of said parent applications now abandoned.

It has been known for some time that organosiloxanes could be applied to paper to prevent adhesion of sticky materials thereto. Consequently, siloxane treated paper has been used as interleaving for adhesive tapes and in the packaging of materials which normally adhere to paper. In the past, the siloxanes which were most widely applied to paper were methylhydrogenpolysiloxanes or trimethyl endblocked dimethylpolysiloxane fluids or combinations thereof. In addition, it has also been suggested in U.S. Patent 2,807,601 that mixtures of hydroxylated dimethylpolysiloxanes and methylhydrogenpolysiloxanes containing at least 5% by weight methylhydrogen could be employed to treat paper.

All of these compositions give release of adhesives from the paper. However, they suffer from a serious disadvantage, namely, that some of the siloxane is transferred from one layer of paper to another when the paper is in a roll. As is well known, in the fabrication of paper the paper is prepared and then given any necessary treatments and thereafter rolled and stored until it is to be used for the fabrication of articles. When the paper is in a roll, one side of the paper is, at various points, in contact with the other side. Consequently, any material which is applied to one side can transfer to the other side. This is precisely what has happened with all heretofore employed siloxanes.

This transfer of the siloxane from one side of the paper to the other has prohibited the use of siloXane treated papers in the manufacture of those articles which require lamination of the paper. For example, in the manufacture of many types of containers, paper is laminated to paperboard by means of an adhesive. If the paper has been previously treated with a siloxane which gets on both sides of the paper, the latter cannot be successfully laminated because it will release from the paperboard. On the other hand, if a siloxane could be applied to one side of the paper and not transferred to the other side, it would be possible to laminate the untreated side of the paper. With such paper it is possible to prepare cardboard cartons or other laminated paper cartons with the treated side of the paper on the inside of the carton and thereafter obtain release of any adhesive material which is placed in the carton. Such an article would be highly desirable for the packaging of such'materials as frozen foods, asphalt, resins, pitch, sticky gum-s and rubbers and other adhesive materials. This invention produces such an article.

It is the object of this invention to produce a paper article coated with a silicone, which paper can be rolled without transfer of the silicone to the untreated side of the paper. Another object is to provide a treated paper which can be laminated and at the same time give excellent release from the exposed surface. Another object is to prepare a paper from which better release is obtained than with heretofore known siloxanes. Another object is to provide a method of treating any organic solid surface. Other objects will be apparent from the following description.

This invention relates to a paper which is coated with at least .1% by weight based on the weight of the paper of an organopolysiloxane obtained by curing a mixture of siloxanes consisting essentially of from .1 to 3% by weight of methylhydrogenpolysiloxane and from 97 to 99.9% by weight of asiloxane of the formula (CH2) xSlO L in which x has a value from 1.9 to 2 inclusive and in which siloxane substantially all of the molecules have attached thereto at least a total of two silicon-bonded hydroXyl groups and/or alkoxy groups of less than 5 carbon atoms.

The paper of this invention is best prepared by applying thereto a solution or an emulsion of the polysiloxane mixture. Preferably the solution or emulsion should contain from 1 to 10% by weight of the polysiloxane. After the paper has been treated with the siloxane dispersion, it is then cured by heating. The treated paper should have at least .1% by weight siloxane thereon. The upper limit of the amount of silicone is not critical although there is little to be gained by employing more than 5% by weight siloxane.

In order to hasten the cure it is desirable to employ a curing catalyst. The preferred catalysts are the metal salts of carboxylic acids such as lead octoate, dibutyltindiacetate, dibutyltindilaurate, zinc octoate, ferric octoate, ferric naphthena-te, cobalt naphthenate and the like.

If it is desired to treat the paper on one side only, the preferred method is to spray one side of the paper with the siloxane solution or emulsion as it comes from the size press. The paper can then be passed over drying drums where the siloxane cures and then into rolls which can be stored for long periods of time without transfer of the silicone to the untreated side.

The methylhydrogenpolysiloxane must be employed in amount from .1 to 3% by weight based on the weight of the total siloXane. When less than .1% by weight is employed, the curing of the siloxane on the paper is too slow to be of practical importance. It should be understood that if the cure is incomplete there will be a transfer of the siloxane on the paper. Furthermore, insuflicient cure gives poor release. The viscosity of the methylhydrogensiloxane is not critical.

if the amount of methylhydrogensiloxane is 5% or greater, inferior release is obtained. The term methylhydrogenpolysiloxane as employed herein includes both siloxanes of the unit formula (CHQHSiO and copolymers of (CHQHSK) with (Cl-I SiO The non-hydrogenated siloxanes employed herein can be either hydroxylated or alkoxylated homopolymers of dimethylsiloxanes or hydroxylated or alkoxylated copolymers of dimethylsiloxane and monomethylsiloxane or these homopolymers or copolymers containing both hydroxyl and alkoxyl groups. In all cases substantially all of the molecules should have at least a total of two silicon-bonded hydroxyl and/ or alkoxyl groups attached thereto. The term substantially all means that there may be present small amounts of siloxanes which contain neither silicon-bonded hydroxyl nor alkoxyl groups and which are normally present in the production of hydroxylated and/or alkoxylated siloxanes. However, if the amount of non-hydroxylated non-alkoxylated siloxane exceeds 5 to 10%, poor curing and transfer of the siloxane results.

The non-hydrogenated siloxanes of this invention can range in voscosity from fluids of 100 c.p.s. up to nonfiowing soluble gums. These materials may be representcd by the formulae or mixtures of molecules of these types where R is the methyl, ethyl, propyl or butyl radical. The presence of alkoxyl radicals stabilizes the ultimate mixture by substantially reducing the tendency of the ultimate mixture to gel on standing. The fastest curing mixture employs a hydroxylated siloxane at the sacrifice of shelflife or bath-life. The most stable mixture employs a completely alkoxylated siloxane at the sacrifice of cure time. Generally the relative amounts of hydroxyl and alkoxyl groups in this siloxane ingredient are adjusted to give what are considered to be optimum properties for each set of application conditions.

When the viscosity of the siloxane mixture is in the range from 100 c.p.s. to 500,000 c.p.s. the siloxane is best applied to the paper in the form of an aqueous emulsion. These emulsions can be prepared by emulsifying the siloxane mixture with water in the conventional manner of emulsifying siloxanes. In general, the emulsion should be applied to the paper at concentrations of 1 to by weight siloxane. However, higher percentages may be employed if desired.

It should be understood that when the catalyst is added to the emulsion the latter must be used in a reasonable length of time, otherwise the setting of the siloxane will occur in the emulsion which results in an undesirable product. The applicant has found, however, that if small amounts of carboxylic acids are added to the emulsion, the stability is greatly increased. For example, a typical emulsion employing a hydroxylated siloxane and containing a dibutyltindioctoate catalyst is stable for about 30 minutes. In the presence of say 1% acetic acid the same emulsion is stable for at least 8 hours. The stabilization here applies to the methylhydrogenpolysiloxane component. To achieve such stabilization any carboxylic acid may be employed in amount from 0.01 to 2% by weight acid based on the Weight of the emulsion. Preferably, however, the acid should be volatile so that it is removed along with the water when the paper is treated and the siloxane cured. For that reason the preferred acids are acetic, formic, propionic, octanoic, Z-ethylhexoic and the like. The use of alkoxylated siloxanes reduces the need for these acid stabilizers.

When the viscosity of the siloxane mixture is 500,- 000 cps. or above it is preferable to employ the siloxane in the form of a solution. However, it is not essential that such be done since the solution itself can be emulsified if desired. Furthermore, it is essential that solutions be employed on certain types of paper such as glassine. Also it has been found that the solutions of the higher molecular weight siloxanes give better results than solutions of the lower molecular weight siloxanes due to the fact that the latter tend to streak when applied to the paper. Thus, the siloxanes below 500,000 cps. viscosity are best applied as emulsions.

If desired, the siloxane mixtures of this invention can be employed in conjunction with organic resins. The type of organic resins which are most effective are those which cause the silicone to be deposited on the surface of the treated paper. In other words, the organic resin acts as if it were preferentially absorbed on the paper thereby allowing the silicone to be concentrated on the surface. The beneficial effect of the use of organic resins is shown in two ways. On porous paper such as kraft, the resin retards or prevents the absorption of the silicone into the paper. Thus, more silicone remains on the surface of the paper and the release is thereby greatly improved for any given amount of silicone employed. Another effect is shown on all kinds of paper, namely, that with the organic resin, less silicone is needed for a given release.

Resins which give these beneficial effects are aminoplastic resins such as melamine formaldehyde or urea formaldehyde resins and phenol aldehyde resins such as phenol formaldehyde resins. The organic resins may be either water soluble or solvent soluble. In general, water soluble resin are employed in conjunction with the siloxane emulsions. Solvent soluble resins are preferred when the organosiloxane mixture is employed in the form of an organic solvent solution. The organic resin can be applied to the paper either before application of the organosiloxane or simultaneously with the siloxane. For example, a water soluble urea formaldehyde resin may be added to the organo-siloxane emulsion and the mixture applied directly to the paper.

The ratio of organosiloxane mixture to organic resin is not critical and can vary over a wide range. For example, the weight ratios may vary from 1 part by weight silicone to 10 parts by weight organic resin to 10 parts by weight silicone to 1 part by weight organic resin.

The compositions of this invention are applicable to any type of paper such as glassine, parchment, kraft, tissue and the like. The treated articles of this invention are useful in the fabrication of containers of all kinds and are uniquely useful in the fabrication of laminated containers from which it is desirable to obtain release from one surface.

The compositions may also be used advantageously on organic 'plastic surfaces such as nylon, orlon, terephthalic-alkylene glycol esters, cellophane, vinyl plastics and the like.

The following examples are illustrative only and should not be construed as limiting the invention which is properly delineated in the appended claims. All viscosities were measured at 25 C.

The release properties of the paper shown in the following examples were determined by pressing one inch wide medical adhesive tape against the treated surface of the paper with a pressure of 4 lb. per sq. in. for 20 hours at room temperature. The tape was then pulled at an angle of 180 to the surface of the paper at a rate of 12 inches per minute and the force required to do this was determined by means of a spring balance and is expressed as grams per inch width of tape.

EXAMPLE 1 A mixture of 1% by weight of a trimethylsiloxy-endblocked methylhydrogenpolysiloxane fluid and 99% by weight of a 3,000 cps. hydroxylated dimethylpolysiloxane fluid was dissolved in a mixture of toluene and perchloroethylene to give a solution containing by weight silicone. This solution was emulsified in the conventional manner to give a 40% by weight silicone-in-water emulsion. The emulsion was then diluted to 1% by weight silicone and an emulsion of zinc octoate and dibutyltindiacetate was then added in amount to give 2% by weight zinc and .34% by weight tin based on the weight of the silicone in the emulsion. Bleached parchment paper was then immersed in the emulsion, removed therefrom and heated 2 minutes at 235 F. Adhesive tape was released therefrom by force of 10 g. per inch. The same tape released from the untreated paper with a force of 300 g. per inch of width.

EXAMPLE 2 of Example 1.

5 EXAMPLE 3 identical results were obtained when a mixture of 3% by weight of trimethylsiloxy-endblocked methylhydrogenpolysiloxane and 97% by weight of a 1,039 cps. viscosity hydroxylated fluid having the composition 99 mol percent dimethylsiloxane and 1 mol percent monomethylsiloxane was employed in the method of Example 1.

EXAMPLE 4 This example shows the effect of organic canbo-xylic acids on the emulsions of this invention. An emulsion was prepared having an identical composition with that of Example 1. It was divided into several portions. To one portion 1% by weight acetic acid based on the weight of the emulsion was added. To another portion .15 by weight 2-ethylhexoic acid was added to the emulsion. To another portion no acid was added. Immediately after preparing the emulsions each was applied to parchment paper and tested in the manner of Example 1. The emulsions were then allowed to stand 8 hours and again applied to parchment paper and tested in the manner of Example 1. The results are shown in the table below.

Force Required to Release T ape This example illustrates the applicability of the method of this invention to commercial operation. Parchment paper was passed continuously through size press rolls. A by weight silicone emulsion identical in composition with that of Example 1 was applied to one side of the paper. The paper was then passed over drying drums where it was heated for 1 minute at 240 F. The treated paper was then rolled and stored overnight. The next day the paper was rewound into rolls and after tWo days it was unwound from the rolls and laminated with paperboard. During the lamination the untreated side of the paper was glued to the paperboard and there was excellent adhesion to the paperboard showing that there had been no transfer of silicone while the paper was in the roll. The treated side of the paper which was not against the paperboard gave excellent release from various adhesives showing that it had not been de-leteriously affected by the laminating process.

EXAMPLE 6 Percent by weight Force in g.

methylhydrogensiloxane: per inch of width 1 40 3 65 5 85 EXAMPLE 7 A mixture of 3% by weight of trimethylsiloxy-end blocked methylhydrogensiloxane and 97% by weight of a 10,000,000 cps. hydroxylated dimethylsiloxane gum was 6 dissolved in heptane to form a 5% by weight solution. 3% by weight dibutyltindioctoate based on the weight of the siloxane was then added. The solution was applied to glassine paper and the treated paper was cured 1 minute at 235 F. Adhesive tape released from the paper at a force of 10 g. per inch.

EXAMPLE 8 This example shows the eifect of employing organic resins in conjunction with the organosiloxane.

The siloxane employed in this example 'hada composition of 97% by weight of a 3,000 cps. hydroxylated dimethylpolysiloxane fluid and 3% by weight of a trimethylsiloxy endblocked methylhydrogenpolysiloxane. This siloxane mixture was emulsified in water to give 1% by weight total silicone solids based on the weight of the emulsion. A water soluble methylolated alkyl urea resiu having a specific gravity of 1.15 was added to the emulsion in the amounts shown below together with an emulsion of zinc octoate and dibutyltindiacetate'in amount sufiicient to give 2% by weight zinc and .34% by weight tin based on the weight of the total silicone in the emulsion. The emulsion was then applied to parchment paper and the treated paper heated 2 minutes at 235 F. The release qualities of the treated paper were tested employing medical adhesive tape in accordance with the above-described procedure. After stripping from the surface of the treated paper the subsequent adhesion of the adhesive tape Was measured against a steel panel.

Composition Release Subsequent in. g. per adhesion in Percent Percent in. of g. per in. by Wt. by Wt. width of width silicone resin EXAMPLE 9 A series of mixtures were prepared, each containing 3% by Weight of a trimethylsiloxy-endblocked methylhydrogenpolysiloxane fluid. The first mixture contained 97% by weight of a l2001300 cps. fluid mixture of (l) 87 parts by weight of a linear dimethylpolysiloxane having a viscosity of approximately 2000 cps. at 25 C. in which 73% of the endblocking units were methoxyl radicals and 27% of the endblocking units were hydroxyl radicals and (2) 10 parts by weight of hydroxy-endblocked dimethylpolysiloxane fluid having a viscosity of approximately 40 cps. at 25 C. and containing 3.25% by weight silicon-bonded hydroxyl radicals. The second mixture was the same as the first except that siloxane (1) contained 47% rnethoxyl endblocking units and 53% hydroxyl endblocking units. The third mixture and fourth mixtures were the same as the first except that siloxane (1) contained more than ethoxyl and n-butoxyl V endblocking units respectively with the remaining end blocking units beinghydroxyl radicals. The fifth mixture contained 97% by weight of a fluid mixture having a viscosity of approximately 2700 cps. at 25 C. and consisting of (1) 87 parts by weight of a linear dimethylpolysiloxane having a viscosity of approximately 5000 cps. at

spams?- 25 C. and in which over 60% of the endblocking units a were isopropoxyl radicals with the remaining endblocking units being hydroxyl radicals and (2) 10 parts of the above 40 cps. hydroxylated dimethylpolysiloxane.

Each of these mixtures was dissolved in a mixture of 5 toluene and perchloroethylene to give a solution contain-- ing 80% by weight silicone. Emulsions were prepared of each of these solutions according to the method of Example 1. Bleached parchment paper was then immersed in each of the emulsions, removed therefrom and heated 2 minutes at 235 F. Release and subsequent adhesion or transfer properties were then tested as shown in Example 8. The results were as follows:

Release (gjinch) Subsequent l5 adhesion (glinch) Mixture 1 Too small to measure. 7

EXAMPLE 10 I Similar results are obtained when a mixture of 3% by weight of a trimethylsiloxy-endblocked methylhydrogenpolysiloxane fluid and 97% by weight of a 100% methoxy-endblocked 2000 cps. dimethylpolysiloxane is employed in the procedure of Example 9.

That which is claimed is:

1. A method of treating the surface of a solid organic material which comprises applying thereto a dispersion of a mixture consisting of (1) from .1 to 3% by weight based on the total Weight of (1) and (2) of a methylhydrogensiloxane and (2) from 97 to 99.9% by weight based on the total weight of (1) and (2) of a siloxane having a viscosity at 25 C. of at least 100 cps. and having the formula 4 cm) .sI0 0 in which x has a value from 1.9 to 2 inclusive and in which siloxane 2) substantially all of the molecules have attached thereto at least two silicon-bonded radicals selected from the group consisting of hydroxyl and alkoxyl radicals of less than 5 carbon atoms and (3) a curing catalyst for the siloxane and thereafter heating the treated surface to dry it and cure the siloxane.

2. An article of manufacture comprising paper coated with at least .1% by weight based on the weight of the paper of a siloxane coating which was prepared by curing a mixture consisting of (1) from .1 to 3% by weight based on the total weight of (1) and (2) of a methylhydrogensiloxane and (2) from 97 to 99.9% by weight based on the total weight of (1) and (2) of a siloxane having a viscosity at 25 C. of at least 100 cps. and having the formula cm) .sio

in which x has a value from 1.9 to 2 inclusive and in which siloxane (2) substantially all of the molecules have attached thereto at least two silicon-bonded radicals selected from the group consisting of hydroxyl radicals and alkoxyl radicals of less than 5 carbon atoms.

3. An article in accordance with claim 2 in which the paper has been treated on one side only.

4. A dispersion comprising from .1 to 10% by weight of a mixture of siloxanes consisting of (1) from .1 to 3% by weight based on the total weight of 1) and (2) of a methylhydrogenpolysiloxane and (2) from 97 to 99.9% by weight based on the total weight of (1) and (2) of a hydroxylated siloxane having a viscosity at 25 C. of at least 100 cps. and having the formula 7 (CHahSiOij in which x has a value from 1.9 to 2 inclusive and in which siloxane (2) substantially all of the molecules have attached thereto at least two silicon-bonded radicals selected from the group consisting of hydroxyl radicals and alkoxyl radicals of less than 5 carbon atoms, (3) a curing catalyst for the siloxane and (4) from .1 to 2% by weight based on the weight of the siloxane-in-water dispersion of a carboxylic acid.

5. A method of treating the surface of a solid organic material which comprises applying thereto (A) a dispersion of an organosiloxane mixture of (1) from .1 to 3% by weight based on the total weight of (1) and (2) of a methylhydrogensiloxane and (2) from 97 to 99.9% by weight based on the total weight of (l) and (2) of a hydroxylated siloxane having a viscosity at 25 C. of at least 100 cps. and having the formula (CH3) :Si O

in which x has a value from 1.9 to 2 inclusive and in which siloxane (2) substantially all of the molecules have attached thereto at least two silicon-bonded radicals from the group consisting of hydroxyl radicals and alkoxyl radicals of less than 5 carbon atoms, (B) an aminoplast resin in amount such that the weight ratio of the organosiloxane mixture and the aminoplast resin is from 1:10 to 10:1 inclusive, and (C) a curing catalyst for the siloxane, and thereafter heating the treated surface to dry it and cure the siloxane.

6. The method of claim 1 wherein substantially all the molecules of siloxane (2) have at least two siliconbonded hydroxyl groups attached thereto.

7. The article of claim 2 wherein substantially all the molecules of siloxane (2) have at least two siliconbonded hydroxyl groups attached thereto.

8. The dispersion of claim 4 wherein substantially all the molecules of siloxane (2) have at least two siliconbonded hydroxyl groups attached thereto.

9. The method of claim 5 wherein substantially all the molecules of siloxane (2) have at least two siliconbonded hydroxyl groups attached thereto.

10. The method of claim 1 wherein substantially all of the molecules of siloxane (2) have a total of at least two silicon-bonded hydroxyl and methoxyl groups attached thereto.

11. The article of claim 2 wherein substantially all of the molecules of siloxane (2) have a total of at least two silicon-bonded hydroxyl and methoxyl groups attached thereto.

12. The dispersion of claim 4 wherein substantially all of the molecules of siloxane (2) have a total of at least two silicon-bonded hydroxyl and methoxyl groups attached thereto. 1

13. The method of claim 5 wherein substantially all r of the molecules of siloxane (2) have a total of at least two silicon-bonded hydroxyl and methoxyl groups attached thereto.

Referenccs Cited in the file of this patent UNITED STATES PATENTS 2,588,393 Kauppi Mar. 11, 1952 2,612,482 Rasmussen Sept. 30, 1952 2,728,692 Dennett Dec. 27, 1955 2,757,152 Solomon July 31, 1956 9 2,774,690 Cockett Dec. 18, 1956 2,807,601 Dennett Sept. 24, 1957 2,985,545 Leavitt May 23, 1961 OTHER REFERENCES Rochow: Chemistry of the Silicones, 2nd edition, pp. 82, John Wiley & Sons, Inc., New York, 1951. 

4. A DISPERSION COMPRISING FROM .1 TO 10% BY WEIGHT OF A MIXTURE OF SILOXANES CONSISTING OF (1) FROM .1 TO 3% BY WEIGHT BASED ON THE TOTAL WEIGHT OF (1) AND (2) OF A METHYLHYDROGENPOLYSILOXANE AND (2) FROM 97 TO 99.9% BY WEIGHT BASED ON THE TOTAL WEIGHT OF (1) AND (2) OF A HYDROXYLATED SILOXANE HAVING A VISCOSITY AT 25*C. OF AT LEAST 100 CPS. AND HAVING THE FORMULA 